1. Field of the Invention
The present invention relates generally to a rotor design for an internal batch mixer, and more particularly to such a rotor having internal reinforcing ribs.
2. Description of the Prior Art
Large internal batch mixers are used in a variety of applications, one being the mixing of rubber products for tire manufacturing. Such mixers include a pair of rotors which rotate counter to each other within a complementary shaped mixing chamber. The rotors are typically hollow and are water cooled.
Typical examples of such prior art batch mixers are shown in U.S. Pat. No. 5,782,560 to Hatanaka et al.; U.S. Pat. No. 6,494,607 to Valsimis et al.; and U.S. Pat. No. 4,834,543 to Nortey.
These rotors are manufactured from large castings and typically have a central axially extending cavity. It has been known within the prior art to provide straight core ribs which protrude into the internal cavity of the rotors and extend in straight lines parallel to the longitudinal axis of the rotor. A typical example of such prior art rotors with straight core ribs is illustrated in FIG. 3. FIG. 3 is a view from the water end of the left rotor of a rotor pair, with the leading edge of one of the wings of the rotor being located at top dead center. The core ribs are located in the corners of the cavity at the water end cross-section, and extend straight into the plane of the drawing of FIG. 3 and continue parallel to the longitudinal axis of the rotor.
A typical failure mode of rotors of the batch mixers of the type just described is a fatigue failure in the areas of highest stress ultimately resulting in a crack extending through the wall of the rotor and allowing water from the water cooled core to leak into the mixing chamber thus contaminating the rubber mixture or other material being mixed in the batch mixer. There is a continuing need for improvements in rotor design that will extend the working life of such rotors prior to failure.